This application relates to double gear hedge shears. More particularly, it relates to a hedge shear that uses gears between the handles and the blades to improve cutting efficiency.
In the cutting process using traditional hedge shears, branches are collected within the sector covered by the cutting blades at the beginning of the cutting stroke. As the cut proceeds, most of the branches are cut using the outermost parts of the blades. This is a disadvantage, because the force there is at its lowest. Thus, the user of typical hedge shears must apply additional effort to cut branches at the outermost points, resulting in increased strain on the user and inefficiency in the cutting operation.
In most known devices, the force available for cutting remains constant throughout the cutting process. As a result, the amount of output force used when cutting branches is the same as when collecting the branches in the initial stages of the cut. Since collecting the branches requires less force than cutting the branches, a constant output force results in additional inefficiency in the cutting operation.
Gear and linkage systems are widely used in different kinds of cutters. The purpose of these systems is to increase cutting force. This usually also results in increased movement of the handles, which forces the user to extend further than would normally be the case.
The use of gears in hedge shears is known in the art. For example, Gardena sells a geared model which is said to increase the cutting force by 35%. While the Gardena system does increase cutting force, it suffers from a deficiency in that the cutting force remains constant through the cutting process, resulting in the inefficiency described above. In contrast, an efficient pair of hedge shears would perform the collecting stage of the cutting process quickly and with minimum power, while reserving most of the force and handle movement for the cutting stage.
Progressive cutting force systems are also known. Fiskars, the assignee of this application, has U.S. Pat. No. 5,689,888 on such a variable force tool. The gearing is constructed so that there is the greatest force in use when actually needed: in the middle of the branch. This tool makes use of a planetary gear mechanism is ideally suited to cutters where the movement of the handles and blades is asymmetrical. Using such a mechanism with hedge shears is problematic, however, since typically the movement of the blades and handles is symmetrical. Additionally, since head shears generally have symmetrical movement of parts, the parts themselves used to make the shears can be made symmetrical. Fabrication of hedge shears in this manner reduces the manufacturing cost of the shears, since the entire product can be made using only one mold for the blades and one mold for the handles.
Accordingly, there is a need to provide a hedge shear in which the cutting force ratio varies throughout the cut, with the greatest force reserved for the cutting action. Further, there is a need to provide a hedge shear in which the cutting force ratio varies throughout the cut, and where the blades and handles of the hedge shear are symmetrical.
The present invention relates to a cutting tool. The cutting tool includes a first handle having a first gear element and a second handle having a second gear element. The cutting tool also includes a first cutting blade having a third gear element and a second cutting blade having a fourth gear element. The first cutting blade is connected to the first handle, and the second cutting blade is connected to the second handle. The first gear element engages the fourth gear element and the second gear element engages the third gear element.
The present invention also relates to a hedge shear having improved cutting ability. The hedge shear includes a first cutting element, which includes a first handle, a first blade, a first handle gear, and a first blade gear. The hedge shear also includes a second cutting element, which includes a second handle, a second blade, a second handle gear, and a second blade gear. The hedge shear also includes a connector for pivotably connecting the first and second cutting elements such that the first handle gear engages the second blade gear and the second handle gear engages the first blade gear.
The present invention also relates to a cutting tool having two sets of meshing gears for generating increased output force. The cutting tool includes first and second handles, where the first handle includes a first handle gear and the second handle includes a second handle gear. The cutting tool also has first and second blades, where the first blade includes a first blade gear and the second blade includes a second blade gear. The first and second handle gears and first and second blade gears are symmetrical. The cutting tool also includes means for attaching the first handle to the first blade and the second handle to the second blade and means for pivotably connecting the first blade to the second blade. The first handle gear meshes with the second blade gear and the second handle gear meshes with the first blade gear to increase the cutting force as the first and second blades are moved to a closed position.